test: add example test for change_detection

modules/test_lib/src/test_lib.dart

@@ -1 +1,4 @@
-export 'package:guinness/guinness.dart' show describe, ddescribe, it, iit, beforeEach, afterEach, expect;
+export 'package:guinness/guinness.dart' show
+    describe, ddescribe, xdescribe,
+    it, xit, iit,
+    beforeEach, afterEach, expect;

modules/test_lib/src/test_lib.es6

@@ -1,6 +1,8 @@
 export var describe = window.describe;
+export var xdescribe = window.xdescribe;
 export var ddescribe = window.ddescribe;
 export var it = window.it;
+export var xit = window.xit;
 export var iit = window.iit;
 export var beforeEach = window.beforeEach;
 export var afterEach = window.afterEach;